Adjust README file + remove unnecessary /docs directory (Sylius#389)

| Q               | A
| --------------- | -----
| Branch?         | 2.0
| Bug fix?        | no
| New feature?    | no
| Related tickets |

Author: GSadee

README.md

@@ -3,54 +3,41 @@
         <picture>
           <source media="(prefers-color-scheme: dark)" srcset="https://media.sylius.com/sylius-logo-800-dark.png">
           <source media="(prefers-color-scheme: light)" srcset="https://media.sylius.com/sylius-logo-800.png">
-          <img alt="Sylius Logo." src="https://media.sylius.com/sylius-logo-800.png">
+          <img alt="Sylius Logo" src="https://media.sylius.com/sylius-logo-800.png">
         </picture>
     </a>
 </p>
-<br/>
+
+<h1 align="center">PayPal Plugin</h1>
+
 <p align="center">
-    <a href="">
-        <img src="https://www.paypalobjects.com/webstatic/mktg/Logo/pp-logo-200px.png" width="200" />
-    </a>
+  <a href="https://sylius.com/plugins/" target="_blank">
+    <img src="https://sylius.com/assets/badge-official-sylius-plugin.png" width="200" alt="Official Sylius Plugin">
+  </a>
 </p>
-<br/>
+
 <p align="center">
-    <a href="https://sylius.com/plugins/" target="_blank">
-        <img src="https://sylius.com/assets/badge-official-sylius-plugin.png" width="150">
-    </a>
+  Official plugin for 
+  <a href="https://www.paypal.com/uk/business/platforms-and-marketplaces" target="_blank">PayPal Commerce Platform</a>
+  – the newest and most advanced of PayPal solutions.
 </p>
 
-# PayPal Plugin
+---
 
-Sylius Core Team’s plugin for [PayPal Commerce Platform](https://www.paypal.com/uk/business/platforms-and-marketplaces) - the newest and most advanced of PayPal solutions.
+## Documentation
 
-#### Why should I use PayPal in my online business?
+📖 Full documentation is available here:
+👉 [PayPal Plugin Documentation](https://docs.sylius.com/paypal-plugin)
 
-* one of the most popular payment methods in the world;
-* worldwide network of 280+ millions consumers and 24+ millions merchants;
-* bank payouts are available in U.S., U.K., the E.U., Australia, and Canada;
-* PCI DSS and 3DS 2.0 compliance
-* full risk management, incl. customisable fraud tools & insight and dispute resolution via dynamic APIs.
+## Security issues
 
-#### What does this plugin give me?
+If you think that you have found a security issue, please do not use the issue tracker and do not post it publicly.
+Instead, all security issues must be sent to `security@sylius.com`
 
-* official payment integration developed and maintained by the Sylius Core Team;
-* global support for over 100 currencies across 200+ markets;
-* two-side operations between Sylius & PayPal administration panels (payments, refunds, reports, etc.);
-* better conversion thanks to direct checkout from both product & cart page;
-* support for all credit & debit cards;
-* popular regional payment methods, i.e. iDeal, SEPA, Sofort, eps, Griopay or Przelewy24;
-* direct PayPal transactions with PayPal wallet
+## Community
 
-1. [Installation](docs/installation.md)
-1. [PayPal environment](docs/sandbox-vs-live.md)
-1. [Onboarding](docs/onboarding.md)
-1. [Reports](docs/reports.md)
-1. [Processing payments](docs/processing-payments.md)
-1. [Development](docs/development.md)
+For online communication, we invite you to chat with us and other users on [Sylius Slack](https://sylius.com/slack).
 
-#### Supported branches
+## License
 
-* `1.5` (v1.5.*) - security fixes
-* `1.6` (v1.6.*) - bug fixes, improvements
-* `1.7` (v1.7.*) - new features
+This plugin is released under the [MIT License](LICENSE).